This invention concerns a method to produce shaped multi-layer plates, the relative plant for their production and also the shaped multi-layer plates obtained thereby, as set forth in the respective main claims.
The invention is applied in the production of shaped multi-layer plates employed in the field of building construction, principally as modular elements to provide a mantle or covering.
The multi-layer plates can also be applied in other fields, such as for example furnishings or accessories.
The state of the art covers modular plates used to cover large areas such as, for example, warehouse roofs, industrial buildings, schools, etc.
Compared with traditional coverings such as tiles, flat tiles, etc., these modular plates are less expensive, quicker to install, have better mechanical characteristics, such as weight, good resistance to shocks, and to atmospheric agents, etc. Moreover, the plates make it possible to achieve extremely complex shapes and to cover extremely sharp inclines.
At the present time, these modular plates are made of metal, for example, copper, zinc-plated or stainless steel, aluminium etc., or by using other materials such as synthetic resins, or also fibre cement or asbestos cement.
Plates made of synthetic resins are lighter and more resistant to corrosion, are less heat conductive, easier to work and offer a greater variety in terms of appearance and finishing.
Plates made of fibre cement, or asbestos cement, which are sold under the names of Eternit(copyright), Amiantit(copyright), Solonit(copyright), Fibronit(copyright) etc., have the disadvantage that with time they lose their original compactness and release into the environment the mineral fibres which they contain.
The prolonged action of atmospheric agents, differences in temperature, erosion caused by the wind, acid rain and the proliferation of vegetal microorganisms, cause in the long term a deterioration of the plates.
At the present time, there is the appropriate legislation which imposes the disposal of coverings made in asbestos cement in order to eliminate the spread into the environment of asbestos fibres and dust, which are particularly harmful to man.
Of the various disposal techniques, there is one known to the state of the art whereby covering plates made of synthetic thermoplastic resins are applied on top of the fibre cement or asbestos plates. These resins normally include reinforced polyesters, polyvinyl chloride (PVC) polymethylmethacrylate (PMMA) or other similar compounds.
Apart from eliminating pre-existing roof coverings, these synthetic resin plates are also used as primary building elements to make new coverings.
The plates are usually produced by a process of extrusion, using a single type of material, or by means of co-extrusion using materials with different bases so as to achieve a multi-layer.
In this last case, the state of the art includes, for example, plates or panels including at least an inner layer which has a supporting and stiffening function, whereas the outer layers have a covering function, thus providing an aesthetic appearance and high resistance to atmospheric agents.
In order to make them more rigid, and to form obligatory routes which will deliver the rain water to the gutter, the multi-layer plates are shaped with a form like a wave, or fretted or otherwise.
In production methods known to the state of the art, the plates are shaped directly during the step of extrusion, or of co-extrusion, by an extrusion head with lips which have an outlet in the shape desired for the plate.
According to another technique, the plates are shaped downstream of the extrusion machine, by sizing-shaping rollers placed immediately at the outlet of the extrusion head.
In both cases, the plates are shaped when the plastified material is not yet stabilized thermally, dimensionally and chemically.
This means that the overall thickness and/or the thickness of the individual plates, is not uniform over all the surface of the multi-layer plates; it therefore follows that in some areas the plate does not have the required characteristics, and is therefore more fragile and vulnerable to the atmospheric agents. Moreover, as the shaping is carried out when the plastifed material is not yet perfectly stabilized, the layers slip against each other and cause surface tensions which cause plates to be created with irregular and discontinuous surfaces.
In some segments, especially if the outer layers are of a limited thickness, fissures, cracks or microcraters are generated. These make the inner layers too close to the surface, and these are often not suitable to be exposed to the atmospheric agents. The plates themselves are also structurally weakened.
To overcome this disadvantage, it is often necessary to oversize the thickness of the individual layers, but this causes an increase in the costs of production, the weight of the plate, in adaptability and other problems.
Another shortcoming is the early wear caused by thermal stress to which the sizing-shaping rollers are subject, because of their position at the outlet of the extruder head. This early wear affects the shaped plate and causes a dimpling effect on the surface layers and thus the inner layers are revealed.
In some applications, for example in roof coverings on buildings for the food or textile industry, the layer facing the inside of the building is covered with a layer of non-fabric fabric, or other similar or comparable material, in order to prevent drops of condensation from forming which could contaminate the products made in such buildings.
At the present time, the layer of non-fabric fabric is associated with the covering plates by gluing; in the long term, this involves poor adhesion and consequently the layer of non-fabric fabric comes unstuck from the covering plate.
Moreover, the non-fabric fabric plate is attached when the multi-layer plate is already stabilized, and at a different step of the production procedure; this causes an increase both in production costs and in production times.
EP-A-0218252 describes a method to obtain multilayer slabs using three extruders coming together at a coextrusion head, from which the multilayer composite is recovered, which is cooled by the rollers of a calender and is drawn by means of a train.
This document does not teach or suggest a method to produce shaped or corrugated plates able to solve the aforementioned problems.
The present applicants have designed, tested and embodied this invention to overcome the shortcomings of the state of the art, and to achieve further advantages.
The purpose of the invention is to provide a method to produce shaped multi-layer plates whether they be flat, undulate or of, any desired shape, able to supply products of a high quality and in limited production times.
Yet another purpose of the invention is to produce shaped multi-layer plates of superior mechanical characteristics and high quality, such as: high structural and surface resistance to stress and destructive agents, lightness, brightness, uniform thickness of all the layers, cohesion between the layers, no cracks, micro-fissures, micro-craters, surface tension.
In the shaped plates according to the invention, the inner layers do not show through, the outer surfaces do not crumble and no powder particles or similar are released into the atmosphere.
Each layer can be of the mono-component or multi-component type.
At least in the case of a multi-component layer, each layer can be obtained by means of extrusion, using a two-stage coextruder, whereby it is possible to eliminate a plurality of operations normally performed before extrusion, such as drying or de-gassing.
The layers are put together by a feeder assembly and then subjected to heating and plastification in an extrusion assembly with a co-extruder head with flat lips.
A continuous and flat-surfaced multi-layer emerges from the co-extrusion head, and is then fed to a calendering assembly which includes at least a pair of stabilizing cylinders.
The flat multi-layer plate emerging from the calendering assembly has a uniform thickness, due to the effect of the stabilizing cylinders. The layers are stabilized and in perfect cohesion, they have a good aesthetic appearance, the right temperature, and the desired consistence and rigidity.
Moreover, thanks to the planarity of the plate, no wrinkle effect is created between the layers and therefore no micro-fissures are created in the outer layers.
According to the invention the flat multi-layer plate emerging from the calendering assembly is fed to an assembly comprising a plurality of shaping rollers, where the plate is thermally adjusted and shaped.
The thermal adjustment and shaping assembly heats the multi-layer plate to and/or maintains it at the appropriate temperature for plastic deformation, and also impresses the desired shape to the plate.
According to the invention, the plate may be shaped lengthwise and/or widthwise, and may have a wave-shaped profile, a fretted profile, a mixed profile or another desired profile.
The shaped multi-layer plate, when it leaves the thermal adjustment and shaping assembly, is cooled, optionally trimmed at the edges and then fed to an assembly for shearing to size.
The multi-layer plates, after shearing to size are then discharged arid accumulated automatically on the appropriate storage surfaces such as, for example, pallets.
According to a variant, upstream of the thermal adjustment and shaping assembly there is an application assembly which associates with the multi-layer plate, by a simple operation of heat cohesion, a supplementary layer of material for protection, finishing, adornment or other, such as for example, non-woven fabric or imitation leather.
According to a first embodiment, the supplementary layer is associated with the flat plate in an intermediate position between the extrusion assembly and the calendering assembly.
According to another embodiment, the supplementary layer is associated with the flat plate in an intermediate position between the calendering assembly and the thermal adjustment and shaping assembly.
According to the invention, the application assembly of the supplementary layer comprises at least a directly heated cylinder and/or a cylinder cooperating with external heating means suitable to raise the temperature of the multi-layer plate to one suitable to apply the protective and/or adornment layer, without the need for additives.
According to the invention, the multi-layer plate includes at least two layers.
In the preferred embodiment of the invention there are at least three layers: one intermediate structural layer and two outer layers, respectively upper and lower.
The intermediate structural layer has the function to guarantee high resistance both mechanical and chemical; according to a variant the intermediate layer is loaded with filling and/or reinforcing materials.
The outer layers have the function to guarantee high resistance to mechanical stresses and, in particular the upper layer has the function to guarantee high resistance to ageing and to deteriorating agents; the upper layer must also have high brightness and shine.
According to the invention, the outer layers are less thick than the intermediate layer.
According to a first embodiment of the invention, the lower layer is made of anti-shock polyvinyl chloride (PVC), for its characteristic of superficial smoothness and pleasant aesthetic appearance.
According to a variant, the lower surface is made of polycarbonate (PC), or high density polyethylene (PEHD), or propylene (PP).
According to one embodiment of the invention, the intermediate layer is made of polyvinyl chloride (PVC), optionally with the addition of semi-expanded material or loaded with filling and/or strengthening materials.
According to a variant, the intermediate layer is made of high density polyethylene (PHD) or polypropylene (PP).
According to another variant, the intermediate layer is made of several differentiated layers, each characterised by a different load or materials.
For strengthening, filling and/or lightening materials for use in the intermediate layer, it is possible to use calcium carbonate (CaCO3), powdered cork, wood chips, granulated cereals, mineral or glass fibres.
According to one embodiment of the invention, the upper layer is made of polymethyl methacrylate (PMMA); this material, apart from being highly resistant, gives a good aesthetic quality because it has a shiny surface and also can be coloured any shade desired, either transparent or opaque (smoked).
According to a variant, the upper layer is made of polycarbonate (PC), or anti-shock polyvinyl chloride (PVC), or in polypropylene (PP) or yet again in acrylonitrile-butadiene-styrene (ABS).